The present invention relates to a control system for an automatic transmission for automobiles, and more particularly to an automatic transmission by means of a belt drive device which is adapted to vary the transmission ratio continuously.
In a conventional belt-drive automatic transmission, which is called a continuously variable transmission, a centrifugal clutch is provided between a crankshaft of an internal combustion engine and an input shaft of the automatic transmission. The centrifugal clutch engages when the engine speed exceeds a predetermined value to transmit the output of the engine to the input shaft of the automatic transmission. On the other hand, the transmission ratio of the transmission changes with an increase of the engine speed and in accordance with load on the engine.
During the driving of a vehicle provided with such a belt-drive automatic transmission, when the vehicle is decelerated by releasing the accelerator pedal, the transmission ratio is increased to meet the decrease of vehicle speed. However, if the accelerator pedal is rapidly released for producing the engine braking effect, a large shock will arise in the power transmission system connected by the centrifugal clutch, since the transmission ratio increases suddenly. Such a shock gives an uncomfortable feeling to passengers.